1. Field of the Invention
The subject of the present invention is a device for storing and mixing two gases or two mixtures of gases under pressure.
More specifically, the invention relates to a device which allows two gases or two mixtures of gases to be stored for the required time under pressure and mixed in given proportions at the time said mixture is to be used.
2. Description of the Related Art
Mixtures with a very low content, for example a few parts per billion (ppb) or fractions of parts per million (ppm) of active gases such as SO2 or NOx are relatively tricky to prepare and to store and often pose problems associated with keeping the mixture in their storage cylinder and of using them in situ.
This is why it has been proposed for this mixture to be prepared using a diluent. In order to implement this technique, it is necessary to have a cylinder of the gas that is to be diluted and its pressure reducer, a cylinder of diluent gas and its pressure reducer, and a diluting mixer. If the time needed to purge the circuits connecting these various components and the cost of these various components are taken into consideration, producing a mixture with a very low content becomes a prohibitive proposition.
One object of the present invention is to provide a device which makes it possible to store and to mix two gases or two mixtures of gases which allows the final mixture to be prepared in situ with an accuracy regarding the proportions of the various components which is at least as good as in the prior art and which allows very low proportions of some of the gases, these being of the order of a fraction of ppm or of a few ppb.
In order to achieve this object according to the invention, the device for storing and mixing two gases or mixtures of gases under pressure comprises:
an outer chamber containing the first of said gases and equipped with an opening;
an inner chamber arranged inside said outer chamber containing the second gas and equipped with an opening;
a two-way valve comprising a body fixed hermetically in the opening of the outer chamber, a first passage having an inner end connected to the opening of the inner chamber and an outer end and equipped with first controllable shut-off means, and a second passage having a first inner end opening into the said outer chamber and a second outer end and being equipped with second controllable shut-off means,
first and second means of adjusting flow rate and pressure, each having an inlet connected to the outer outlet of one of the passages of said two-way valve and an outlet; and
first and second pipes for connecting the outlet of each adjusting means to a single outlet of said storing and mixing device.
It will be understood that the mixture of active gases to be diluted is already diluted in acceptable proportions, for example of the order of a few ppm, in the inner chamber while the outer chamber contains the diluent gas. Given the degree of dilution of the active gases in the inner chamber, the latter can be produced initially with ease and precision and its storage does not pose any particular problems. When using the final mixture, it is possible to mix this in situ by opening the two valves, which makes it possible to obtain, at the outlet of the entire device, the mixture of the active gases in the desired proportions with the desired flow rate and at the desired pressure by virtue of the presence of the reducers and of the calibrated orifices.
As a preference, the mixtures of gas or the gases contained in the two chambers are at the same pressure and the ratio of the volumes of the two chambers is equal to the ratio of the quantities of gas or mixtures of gas to be withdrawn from the two chambers in order to obtain the final mixture.
It should also be emphasized that once the inner chamber and the two-way valve have been fitted inside the outer chamber, the two chambers can easily be conditioned and filled via the two-way valve.